The cigarette filter is a small, cylindrical component found at the end of nearly every manufactured cigarette. It is designed to modify the smoke stream, reducing the amount of particulate matter and gas-phase compounds inhaled from the burning tobacco. Introduced widely in the 1950s, the filter became a standard feature intended to address growing public health concerns. The filter’s structure affects both the composition of the smoke and the smoker’s experience.
Physical Composition and Design
Most modern cigarette filters are constructed from cellulose acetate tow, a synthetic material composed of thousands of fine plastic fibers. This material is secured with a plugwrap paper. Glycerol triacetate, a plasticizer, is often applied to the fibers to help them maintain their shape.
The filter assembly is wrapped in tipping paper, which serves as the mouthpiece. The tipping paper often contains microscopic ventilation holes. These holes allow ambient air to enter the smoke stream, diluting the smoke before it is inhaled.
The Mechanism of Filtration
The filter’s primary action is mechanical separation, capturing smoke particles within the dense network of cellulose acetate fibers. This process occurs through three main mechanisms: inertial impaction, diffusion, and interception.
Inertial impaction happens when larger, heavier particles collide with the fibers. Diffusion is the dominant mechanism for extremely small particles, which move randomly and stick to the fibers. Interception occurs when a particle follows the smoke streamline but is physically intercepted by the fiber.
Although these mechanisms trap a portion of the larger particulate matter, commonly called “tar,” the filter is largely ineffective at removing toxic gaseous components. Examples of these gaseous components include carbon monoxide and formaldehyde.
Influence on Smoke Delivery and Perception
Ventilation holes dramatically change the smoking experience by introducing air to the smoke. This air dilution reduces the concentration of tar and nicotine measured by smoking machines, which was historically used to label cigarettes as “light.” The air also cools the smoke and reduces its harshness, resulting in a perceived smoother taste.
This manipulation of the sensory experience can lead to a change in smoking behavior known as compensation. Smokers may unconsciously inhale more deeply, take more frequent puffs, or block the ventilation holes to achieve the desired nicotine dose. These actions negate the filter’s intended dilution effect.
Health Implications and Misconceptions
The most significant health implication is the widespread misconception that the filter reduces the danger of smoking. Historically, the filter was marketed as a safety feature to protect the smoker from harm. The fact that the filter turns brown was a visual trick to reinforce the false perception that harmful substances were being effectively removed.
Although filters trap some particulate matter, they do not eliminate the thousands of toxic chemicals in tobacco smoke. The dilution caused by ventilation may lead smokers to inhale the smoke deeper into the peripheral regions of the lungs. This behavioral change is hypothesized to be a factor in the increased incidence of adenocarcinoma, a specific type of lung cancer. The filter’s primary function is to make the concentrated smoke more palatable and easier to inhale, facilitating continued use.